CLAYS OF HUNTERDON COUNTY. 425 



HUNTERDON COUNTY. 



The clay deposits of Hunterdon are not extensive, but so far 

 as known, are limited to local accumulations due directly to the 

 disintegration of the underlying rock or to wash from steeper 

 •slopes. In the latter case, the clay is usually residuary material 

 which has been transported at most only a few hundred yards 

 from its source. 



Lamb crtv ill e. — A small deposit of ferruginous brick clay de- 

 rived directly from the decomposition of trap rock is worked on 

 the hill about one mile southeast of Lambertville (Loc. 277). It 

 is rather shallow and contains numerous large bowlders, the dis- 

 integrated portions of the rock ( PL XXIV, Fig. 1 ) . Although 

 the brickyard is a small one and worked intermittently, bricks 

 have been made in this vicinity from this clay since 18 16. There 

 is no likelihood of finding an extensive deposit on this ridge, but 

 clay similar in amount and character probably occurs at many 

 points along the top of Sourland mountain between Lambertville 

 and Neshanic. The material burns red and has a low fire shrink- 

 age. 



Flemington. — A bed of loamy clay ranging from 3 to 7 feet 

 in thickness is worked at Flemington (Loc. 276), for the manu- 

 facture of common brick (PI. XLIV, Figs. 1 and 2). The 

 lower portion of the clay was derived directly from the Triassic 

 red shale, while the upper few feet, which contain occasional 

 pebbles of trap rock, were derived by wash from the steep slopes of 

 a hill of trap rock a few rods west of the clay pits. Both clays are 

 used and burn to a product of good red color and hard body, 

 b>ut they are too gritty for use in draintile. The physical prop- 

 erties of this material are as follows: Water required, 23.9 per 

 cent.; air shrinkage, 3.5 per cent. Average tensile strength 159 

 pounds per square inch. The sample burned as follows : 



Burning tests of a clay from Flemington, Pedrick's yard. 

 Cone 05 13 



Fire shrinkage, i.i % 7.1 % 7-1% 



Absorption, 12.34% 4-94% 3-9% 



Color, red deep red very deep red 



Condition, not quite steel-hard steel-hard 



